This invention relates to fuel controls for turbine types of power plants and particularly to improvements of the type exemplified by U.S. Pat. No. 2,822,666 assigned to the same assignee, and the types typified by the JFC-12, JFC-25, JFC-60 manufactured by Hamilton Standard Division of United Aircraft Corporation.
As is well known in the fuel control art, the fuel control not only serves to control fuel flow but has also been utilized to control many other aspects associated with engine control. As for example, the fuel control may be utilized to control the engine stator vanes, bleed valves or other aspects of the engine. It should be realized that in some applications these functions noted above may be independently controlled. This invention finds utility where the fuel control includes the function of controlling fuel flow to the power plant as well as the function of controlling the stator vanes of the power plant.
In this regard, the invention serves to provide the dual function of automatically resetting idle speed to maintain constant engine power and setting of the position of the variable stator vanes by utilizing a single cam and a single cam follower. This is in contrast to utilizing two cams with two followers or a single cam with two profiles each of which has its own follower.
Additionally, by proper sizing of lever ratios and spring rates the single point contact defines the idle droop schedule.
Another aspect of this fuel control is to provide the W.sub.f /P.sub.3 .times. P.sub.3 fuel control function by utilizing the throttle valve to perform the multiplying. Hence, where it has been customary to utilize a fulcrum lever and force system to accomplish this function this invention contemplates controlling the hydraulic pressure forces acting across the throttle valve and contouring one of its windows in a unique manner to obtain this function.
In this light, the fuel control schedules W.sub.f /P.sub.3 as a function of compressor speed and power lever position for steady state, and as a function of compressor speed, compressor inlet temperature for acceleration and multiplies this value by P.sub.3 in order to achieve effective fuel control while assuring that the engine does not encounter rich or lean blow out, overtemperature and surge.